贵金属在载体上的分布对催化剂性能的影响

Influences of Precious Metal Distributions on Substrates on Catalyst Properties

以Pt,Pd,Rh3种贵金属作为汽油车用三效催化剂的主要催化活性组分,制备了2组具有不同组合与分布形式的分层催化剂和分区催化剂,并通过发动机台架测试系统进行了催化活性评价。通过对表征催化剂催化性能的空燃比特性、起燃特性和催化转化效率的对比分析,研究了3种贵金属的组合与分布对催化剂3大特性的影响。结果表明:贵金属的组合与分布方式会对催化剂的3大特性产生显著影响;贵金属分层分布催化剂与分区催化剂相比具有更高的空燃比特性和起燃特性,其中PtRh(o)/Pd(i)催化剂表现最佳,但贵金属分区催化剂,主要是PtRh组合在近发动机端的分区催化剂,在所有催化剂中表现出最优异的起燃特性;因此,在进行欧3、欧4等车用排放控制系统设计时,可以利用不同贵金属组合与分布催化剂的独特性能优势,在同一载体或同一系统中的不同载体上进行可控的贵金属负载与分布,来提高催化剂的综合性能;以这种方式获得的效果预期比单纯提高贵金属含量获得的效果好得多。

Using precious metals Pt, Pd, Rh as main active components of three-way catalysts for cars, two groups of separate-layer catalysts and separate-area catalysts with different precious metal combinations and distributions on substrates were prepared and their activities were tested on engine bench system. Influences of different combinations and distributions of the three precious metals on the catalysts characteristics were studied by contrasting and analyzing the performances of ratios of air to fuel（A/F）, light-off temperatures and catalytic conversions of the catalysts. The results showed that precious metal combinations and distributions had great effect on the catalysts three characteristics. A/F properties and catalytic conversion efficiencies of the separate-layer catalysts were higher than those of the separate-area catalysts, and those of PtRh（o）/Pd（i） sample were the best in the series of catalysts. However, the separate-area catalyst in the combination of PtRh loaded on the part of the substrate near to engine showed the most excellent light-off performance. So the authors suggested that the full advantages of remarkable properties of the catalysts with different combinations and distributions could be taken in designing automobile emission control systems meeting EuroⅢ or Ⅳ, and the catalysts integration properties would be improved by controlling precious metal loading and distributing on one substrate or one system, and the effects obtained by such way were thought much better than those by increasing precious metal loadings.